I have to ask: what's with all the pictures of Kyon getting slapped around by the girls. There aren't many on Danbooru, but they're all over the place on Pixiv. Is it a meme or something?

I don't know, but it's probably what would happen if SHnY was more grounded or closer to the drama genre. It could also be reaction to how oblivious or how much of an unintentional player he is.

Pixiv user "Kani"(Pixiv ID:1781067) requested many artists to draw these pictures. Perhaps he is a slap fetishist.

Or perhaps he just wanted to see Kyon get smacked REAL bad.